1. Field of Invention
The invention is directed to actuator devices for actuating downhole tools and, in particular, to actuator devices comprising a valve that initially moves slowly until a predetermined point at which time the movement of the valve increases to actuate the downhole tool.
2. Description of Art
Some downhole tools need to be retained in an unset position until properly placed in the well. It is only when they are properly located within the well that the downhole tool is set through actuation of either the downhole tool itself or an actuator device that mechanically moves the downhole tool to its set position. One prior technique for actuating downhole tools is creation of a window or passageway within the downhole tool or actuating device exposing the actuating member, e.g., piston, of the downhole tool or actuating device to the wellbore environment, e.g., the hydrostatic wellbore pressure. The hydrostatic pressure then acts upon the actuating member of the downhole tool to move the actuating member and, thus, the downhole tool, to the set position so that the downhole tool is actuated. In this technique, the creation of the window or passageway does not directly actuate the downhole tool.
In other downhole tools or actuating devices, a fluid pumped down the well is used to break shear pins on the downhole tools which release the actuating member so that the downhole tool is moved to its set position. In still other downhole tools or actuating devices, an explosive charge is detonated by a detonator connected to the surface of the well through an electronic line or connected to battery pack located on the downhole tool or actuating device. The force from the combustion of the explosive charge then acts upon the actuating member and the downhole tool is either directly, or indirectly through the actuating device, actuated.